Many individuals are exposed to hand-induced vibration by using hand-held vibrating or repeated impact-type tools that include, but are not limited to, chipping hammers, jackhammers, riveters, jackleg drills, rotary grinders and sanders, orbital sanders, chain saws, lawn mowers, and engine-powered string trimmers. Individuals can also be exposed to hand-induced vibration through clasping objects in their hands that are being ground, swagged, or repeatedly hammered. Finally, individuals can be exposed to hand-induced vibration while riding motor cycles, motor bikes, all-terrain vehicles, and other like vehicles.
Individuals who are exposed to hand-induced vibration or repetitive impacts over short periods of time can experience tingling and numbness in the fingers and hand fatigue. If individuals are exposed to high levels of hand-induced vibration over prolong periods of time, vibration-induced white fingers (VWF) can develop. This disease results in a destruction of the small blood vessels in the fingers, and it can be debilitating and cause severe pain in extreme cases. The occurrence of tingling, numbness and fatigue in the hand and fingers and of VWF can be minimized by reducing the levels of vibration energy directed into the hands of individuals who use vibrating or repeated impact-type hand tools or who clasp objects that direct vibration or repetitive impacts into the hand.
Vibration levels can be reduced by redesigning the tool or object or by placing a vibration isolation device between the hand and the tool or object that is being clasped by the hand. One of the methods for reducing the vibration energy directed into the hands has been the use of gloves that have an elastomer, foam or rubberlike material placed between the vibrating tool or object and the hand. Another method has involved wrapping the tool handle with an elastomer, foam or rubberlike material which performs the same function as performed by the same material used in a glove. Hand coverings such as gloves and handle coverings made with elastomers or rubberlike materials have proven to be ineffective in significantly reducing the vibration energy transmitted to hands from vibrating hand tools or objects clasped by the hand. To improve the vibration isolation characteristics of gloves with elastomers or rubberlike materials, it is necessary to make the elastomer or rubber pads used in the gloves very thick. This often makes the glove stiff and very difficult to use in clasping a hand tool or other object. Also, using gloves with thick elastomer or rubber pads causes the hands to become fatigued in a very short period of time.
Use of thick elastomers as tool handle coverings has also been problematic. To achieve acceptable comfort in clasping a tool handle with the hand, the overall diameter of the tool handle with an elastomer pad must be held within specified limits, such as a preferred diameter of 1.5 inches. Thick elastomer pads may be bent or wrapped around small diameter handles. Bending or wrapping is often difficult, since the circumference of the inside of the pad in contact with the handle is substantially less than the circumference of the outside of the pad in contact with the hand.
To avoid bending or wrapping problems, thick elastomer pads that are used on small-diameter tool handles may be pre-molded or pre-formed into a cylindrical shape. The pre-molding process is often expensive and restricts the use of a pre-molded or pre-formed pad to a single-size handle and a single handle configuration. In either the wrapped or the pre-molded form, thick elastomers pads used on tool handles also quickly deteriorate under the severe working conditions in which tools exposed to high levels of vibration are commonly used.
Pre-molded elastomer air bladders have been proposed for use in attenuating shock directed into the hand. The injection mold process used to make pre-molded air bladders is very expensive, and as with pre-molded thick elastomer pads, pre-molded elastomer air bladders are restricted to single size and single handle configurations. The bladder material of pre-molded elastomer air bladders is usually fairly thick, such as 0.010 inches or thicker. The increased bladder material thickness significantly reduces the effectiveness of pre-molded air bladders in reducing the vibration transmitted to the hand from a tool handle.
Regardless of whether thick or thin handle coverings are used, and regardless of whether the covering is formed flat or circular, attachment of the handle covering to the handle may be difficult or inefficient. The handle covering needs to be tightly secured to the handle so there is no relative movement between the handle and the handle covering either in a rotational or in an axial sense, while still permitting the radial compression needed for adequate vibration attenuation.
The occurrence of VWF is significantly affected by a cold environment. VWF is more prevalent in areas where workers must work either outside or inside in a cold environment. Gloves are often used in these environments to warm the hands, reducing the effects of cold on the prevalence of VWF in these environments. Using gloves with elastomer or rubberlike pads that are also designed to keep the hands warm creates the same problems that are associated with gloves that have extremely thick elastomer or rubberlike pads. The gloves tend to be stiff and often make it difficult to easily clasp a hand tool or other object.
European standards have recently been promulgated which pose requirements for a protection device marketed in Europe to be properly classified as a "vibration protection glove" or an "antivibration glove." These standards are outlined in European Standard prEN ISO 10819 (1995), Mechanical Vibration and Shock--Hand-arm Vibration--Method for the Measurement and Evaluation of the Vibration Transmissibility of Gloves at the Palm of the Hand. To meet the standard, a glove must have an overall time-averaged vibration transmissibility in the frequency range from 32 Hz to 200 Hz, TR.sub.M, of less than 1.0, and an overall time-averaged vibration transmissibility in the frequency range from 200 Hz to 1,250 Hz, TR.sub.H, of less than 0.6. The vibration transmissibility in the standard is defined as the ratio of the vibration amplitude directed into the palm of the hand with the glove divided by the vibration amplitude directed into the palm of the hand without the glove. The standard specifies that vibration transmissibility is to be measured while the vibration test handle is being clasped with a grip force of 5 lb (25 N) and while the hand is pushing on the vibration test handle with a push force of 10 lb (50 N).
Hand and handle coverings are desired which will more effectively reduce the vibration transmitted to the hand from the hand-held object, and will furthermore be thin, flexible, thermally insulative and relatively inexpensive.